Method and apparatus for generating device-to-device terminal signal in wireless communication system

ABSTRACT

A method of generating a device-to-device (D2D) signal by a user equipment (UE) in a wireless communication system, the method includes mapping a sequence for an automatic gain control (AGC) preamble to a resource element; and generating the AGC preamble by performing an inverse fast Fourier transform (IFFT) on the sequence for the AGC preamble mapped to the resource element, further the sequence for the AGC preamble is repeated N times when mapped to the resource element, and also N is determined based on at least one of a system frequency bandwidth or a transmission frequency bandwidth.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/121,550, filed on Aug. 25, 2016, which is the National Phase of PCTInternational Application No. PCT/KR2015/001790, filed on Feb. 25, 2015,which claims priority under 35 U.S.C. 119(e) to U.S. ProvisionalApplication No. 61/944,553, filed on Feb. 25, 2014, all of which arehereby expressly incorporated by reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, andmore particularly, to a method and apparatus for generating a signal ina device-to-device communication.

Discussion of the Related Art

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.) among them. Forexample, multiple access systems include a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system, and a Multi-Carrier FrequencyDivision Multiple Access (MC-FDMA) system.

D2D communication is a communication scheme in which a direct link isestablished between User Equipments (UEs) and the UEs exchange voice anddata directly with each other without intervention of an evolved Node B(eNB). D2D communication may cover UE-to-UE communication andpeer-to-peer communication. In addition, D2D communication may find itsapplications in Machine-to-Machine (M2M) communication and Machine TypeCommunication (MTC).

D2D communication is under consideration as a solution to the overheadof an eNB caused by rapidly increasing data traffic. For example, sincedevices exchange data directly with each other without intervention ofan eNB by D2D communication, compared to legacy wireless communication,the overhead of a network may be reduced. Further, it is expected thatthe introduction of D2D communication will reduce the power consumptionof devices participating in D2D communication, increase datatransmission rates, increase the accommodation capability of a network,distribute load, and extend cell coverage.

SUMMARY OF THE INVENTION

The technical task of the present invention is to provide a method ofgenerating and transmitting an automatic gain control (AGC) preamble.

Technical tasks obtainable from the present invention are non-limited bythe above-mentioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

In one technical aspect of the present invention, provided herein is amethod of generating a device-to-device (D2D) signal from a userequipment in a wireless communication system, including mapping asequence for an automatic gain control (AGC) preamble to a resourceelement and performing an inverse fast Fourier transform (IFFT) on themapped AGC preamble, wherein the sequence for the AGC preamble isrepeated N times (N>=0) when mapped to the resource element and whereinthe N is proportional to a frequency bandwidth if the user equipment isan in-coverage user equipment.

In another technical aspect of the present invention, provided herein isa user equipment device in a D2D user equipment for generating a D2D(device-to-Device) signal in a wireless communication system, includinga receiving module and a processor, wherein the processor maps asequence for an automatic gain control (AGC) preamble to a resourceelement and performs an inverse fast Fourier transform (IFFT) on themapped AGC preamble, wherein the sequence for the AGC preamble isrepeated N times (N>=0) when mapped to the resource element, and whereinthe N is proportional to a frequency bandwidth if the user equipment isan in-coverage user equipment.

The N may not be related to the frequency bandwidth if strength of asignal received by the user equipment from a base station is equal to orsmaller than a predetermined value.

The frequency bandwidth may include a system bandwidth or a transmissionbandwidth of the D2D signal.

A sequence ID for the AGC preamble may be obtained from asynchronization source of the D2D user equipment.

The sequence ID obtained from the synchronization source may be used incommon by a D2D user equipment having received the AGC preamble.

When a signal transmitted after the AGC preamble is a discovery signalor a communication signal, the sequence ID may be linked to a sequenceID of a demodulation reference signal related to the discovery signal orthe communication signal.

When a cyclic shift is applied to generation of the AGC preamble, thecyclic shift may be linked to a cyclic shift of the demodulationreference signal related to the discovery signal or the communicationsignal.

When a number of sequence IDs of the demodulation reference signalrelated to the discovery signal or the communication signal is greaterthan a number of sequence IDs for the AGC preamble, a modulo operationmay be applied to the sequence ID of the demodulation reference signalrelated to the discovery signal or the communication signal.

A sequence ID for the AGC preamble may be used in common within a grouphaving the D2D user equipment belong thereto.

The sequence for the AGC preamble may include a demodulation referencesignal sequence.

The demodulation reference signal sequence may have a same sequence IDof a demodulation reference signal related to a signal transmitted afterthe AGC preamble.

The sequence for the AGC preamble may include one of a Zadoff-chu (ZC)sequence, a gold sequence and an m-sequence.

According to the present invention, when an automatic gain control (AGC)preamble generated by the present invention is used, the AGC preamblemay also be used for data demodulation, and thus efficiency in the useof resources may increase.

Effects obtainable from the present invention are non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram to describe a structure of a wireless frame.

FIG. 2 is a diagram to describe a resource grid in a downlink slot.

FIG. 3 is a diagram to describe a structure of a downlink subframe.

FIG. 4 is a diagram to describe a structure of an uplink subframe.

FIGS. 5 and 6 are diagrams to describe an automatic gain control (AGC)preamble according to an embodiment of the present invention.

FIG. 7 is a diagram to describe a configuration of atransmitting/receiving device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions or features ofany one embodiment may be included in another embodiment and may bereplaced with corresponding constructions or features of anotherembodiment.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aBase Station (BS) and a User Equipment (UE). The BS is a terminal nodeof a network, which communicates directly with a UE. In some cases, aspecific operation described as performed by the BS may be performed byan upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point(AP)’, etc. The term ‘relay’ may be replaced with the term ‘Relay Node(RN)’ or ‘Relay Station (RS)’. The term ‘terminal’ may be replaced withthe term ‘UE’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’,‘Subscriber Station (SS)’, etc. In addition, in the followingembodiments, the term “base station” may mean an apparatus such as ascheduling node or a cluster header. If the base station or the relaytransmits a signal transmitted by a terminal, the base station or therelay may be regarded as a terminal.

The term “cell” may be understood as a base station (BS or eNB), asector, a Remote Radio Head (RRH), a relay, etc. and may be acomprehensive term referring to any object capable of identifying acomponent carrier (CC) at a specific transmission/reception (Tx/Rx)point.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed for at least one of wireless access systems,Institute of Electrical and Electronics Engineers (IEEE) 802, 3rdGeneration Partnership Project (3GPP), 3GPP Long Term Evolution (3GPPLTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are notdescribed to clarify the technical features of the present invention canbe supported by those documents. Further, all terms as set forth hereincan be explained by the standard documents.

Techniques described herein can be used in various wireless accesssystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier-FrequencyDivision Multiple Access (SC-FDMA), etc. CDMA may be implemented as aradio technology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications (GSM)/General Packet Radio Service(GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may beimplemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a partof Universal Mobile Telecommunications System (UMTS). 3GPP LTE is a partof Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA fordownlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.WiMAX can be described by the IEEE 802.16e standard (WirelessMetropolitan Area Network (WirelessMAN)-OFDMA Reference System) and theIEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity,this application focuses on the 3GPP LTE and LTE-A systems. However, thetechnical features of the present invention are not limited thereto.

LTE/LTE-A Resource Structure/Channel

With reference to FIG. 1, the structure of a radio frame will bedescribed below.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) wirelesspacket communication system, uplink and/or downlink data packets aretransmitted in subframes. One subframe is defined as a predeterminedtime period including a plurality of OFDM symbols. The 3GPP LTE standardsupports a type-1 radio frame structure applicable to Frequency DivisionDuplex (FDD) and a type-2 radio frame structure applicable to TimeDivision Duplex (TDD).

FIG. 1(a) illustrates the type-1 radio frame structure. A downlink radioframe is divided into 10 subframes. Each subframe is further dividedinto two slots in the time domain. A unit time during which one subframeis transmitted is defined as a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms in duration and one slot may be 0.5 msin duration. A slot includes a plurality of OFDM symbols in the timedomain and a plurality of Resource Blocks (RBs) in the frequency domain.Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbolrepresents one symbol period. An OFDM symbol may be referred to as anSC-FDMA symbol or symbol period. An RB is a resource allocation unitincluding a plurality of contiguous subcarriers in a slot.

The number of OFDM symbols in one slot may vary depending on a CyclicPrefix (CP) configuration. There are two types of CPs: extended CP andnormal CP. In the case of the normal CP, one slot includes 7 OFDMsymbols. In the case of the extended CP, the length of one OFDM symbolis increased and thus the number of OFDM symbols in a slot is smallerthan in the case of the normal CP. Thus when the extended CP is used,for example, 6 OFDM symbols may be included in one slot. If channelstate gets poor, for example, during fast movement of a UE, the extendedCP may be used to further decrease Inter-Symbol Interference (ISI).

In the case of the normal CP, one subframe includes 14 OFDM symbolsbecause one slot includes 7 OFDM symbols. The first two or three OFDMsymbols of each subframe may be allocated to a Physical Downlink ControlCHannel (PDCCH) and the other OFDM symbols may be allocated to aPhysical Downlink Shared Channel (PDSCH).

FIG. 1(b) illustrates the type-2 radio frame structure. A type-2 radioframe includes two half frames, each having 5 subframes, a DownlinkPilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot TimeSlot (UpPTS). Each subframe is divided into two slots. The DwPTS is usedfor initial cell search, synchronization, or channel estimation at a UE.The UpPTS is used for channel estimation and acquisition of uplinktransmission synchronization to a UE at an eNB. The GP is a periodbetween an uplink and a downlink, which eliminates uplink interferencecaused by multipath delay of a downlink signal. One subframe includestwo slots irrespective of the type of a radio frame.

The above-described radio frame structures are purely exemplary and thusit is to be noted that the number of subframes in a radio frame, thenumber of slots in a subframe, or the number of symbols in a slot mayvary.

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot. A downlink slot includes 7 OFDM symbolsin the time domain and an RB includes 12 subcarriers in the frequencydomain, which does not limit the scope and spirit of the presentinvention. For example, a downlink slot may include 7 OFDM symbols inthe case of the normal CP, whereas a downlink slot may include 6 OFDMsymbols in the case of the extended CP. Each element of the resourcegrid is referred to as a Resource Element (RE). An RB includes 12×7 REs.The number of RBs in a downlink slot, NDL depends on a downlinktransmission bandwidth. An uplink slot may have the same structure as adownlink slot.

FIG. 3 illustrates the structure of a downlink subframe. Up to threeOFDM symbols at the start of the first slot in a downlink subframe areused for a control region to which control channels are allocated andthe other OFDM symbols of the downlink subframe are used for a dataregion to which a PDSCH is allocated. Downlink control channels used inthe 3GPP LTE system include a Physical Control Format Indicator CHannel(PCFICH), a Physical Downlink Control CHannel (PDCCH), and a PhysicalHybrid automatic repeat request (HARQ) Indicator CHannel (PHICH). ThePCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH delivers an HARQACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled Downlink Control Information (DCI). The DCI transports uplink ordownlink scheduling information, or uplink transmission power controlcommands for UE groups. The PDCCH delivers information about resourceallocation and a transport format for a Downlink Shared CHannel(DL-SCH), resource allocation information about an Uplink Shared CHannel(UL-SCH), paging information of a Paging CHannel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a Random Access Responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, Voice Over Internet Protocol (VoIP) activation information,etc. A plurality of PDCCHs may be transmitted in the control region. AUE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregatingone or more consecutive Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE includes a plurality of REgroups. The format of a PDCCH and the number of available bits for thePDCCH are determined according to the correlation between the number ofCCEs and a coding rate provided by the CCEs. An eNB determines the PDCCHformat according to DCI transmitted to a UE and adds a Cyclic RedundancyCheck (CRC) to control information. The CRC is masked by an Identifier(ID) known as a Radio Network Temporary Identifier (RNTI) according tothe owner or usage of the PDCCH. If the PDCCH is directed to a specificUE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If thePDCCH is for a paging message, the CRC of the PDCCH may be masked by aPaging Indicator Identifier (P-RNTI). If the PDCCH carries systeminformation, particularly, a System Information Block (SIB), its CRC maybe masked by a system information ID and a System Information RNTI(SI-RNTI). To indicate that the PDCCH carries a Random Access Responsein response to a Random Access Preamble transmitted by a UE, its CRC maybe masked by a Random Access-RNTI (RA-RNTI).

FIG. 4 illustrates the structure of an uplink subframe. An uplinksubframe may be divided into a control region and a data region in thefrequency domain. A Physical Uplink Control CHannel (PUCCH) carryinguplink control information is allocated to the control region and aPhysical Uplink Shared Channel (PUSCH) carrying user data is allocatedto the data region. To maintain the property of a single carrier, a UEdoes not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UEis allocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Acquisition of Synchronization of D2D UE

Hereinafter, acquisition of synchronization between UEs in a D2Dcommunication will be described based on the above description and theexisting LTE/LTE-A system. In an OFDM system, when time and frequencyare not synchronized, a multiplexing between different UEs in the OFDMsignal may become impossible due to an inter-cell interference.Individual synchronization of all UEs by direct transmission andreception of synchronization signals of the UEs is inefficient.Therefore, in a distributed node system such as D2D, a certain node maytransmit a representative synchronization signal and the remaining UEsmay be synchronized according thereto. Namely, a scheme where some nodes(at this time, a node may also be referred to as an eNB, an UE, asynchronization reference node (SRN) or a synchronization source)transmit a D2D synchronization signal (D2DSS) for transmission andreception of a D2D signal and the remaining UEs are synchronizedaccording thereto so as to transmit and receive the signal may be used.

The D2D synchronization signal may include a primary D2DSS (PD2DSS) anda secondary D2DSS (SD2DSS). The PD2DSS may be of a structure similarto/modified from a Zadoff-chu sequence or a PSS of a predeterminedlength or a repeated structure thereof. The SD2DSS may be of a structuresimilar to/modified from M-sequence or SSS or a repeated structurethereof. If UEs are synchronized from an eNB, SRN becomes the eNB, andD2DSS becomes the PSS/SSS. A physical D2D synchronization channel(PD2DSCH) may be a (broadcast) channel through which basic (system)information (e.g., information related to D2DSS, a duplex mode (DM), TDDUL/DL configuration, resource pool-related information, D2DSS-relatedapplication type, and the like), which the UE first needs to know, istransmitted. The PD2DSCH may be transmitted on the same subframe as inthe D2DSS or a subframe following the D2DSS.

A SRN may be a node that transmits a D2DSS and a PD2DSCH. The D2DSS maybe of a certain sequence form or may be a sequence indicating certaininformation or of a codeword form after going through a predeterminedchannel coding. In this case, the SRN may be an eNB or a specific D2DUE. In the case of a partial network coverage or out-of-networkcoverage, the UE may become the SRN. Further, in the case of anintercell discovery, the UE may relay a D2DSS at the point of time whena certain offset is added to the point of time when adjacent cell UEsreceive from the SRN in order for the UEs to recognize the timing.Namely, the D2DSS may be relayed through a multi hop. If the relayed UEsare plural or there are a plurality of clusters around, the UE receivingthe D2DSS may observe a plurality of D2DSS and may receive a D2DSShaving different hops.

As described above, such information as types of applications related tothe D2DSS, DM, and the like may be transmitted through the PD2DSCH.However, in some cases, it may be necessary to indicate DM, types ofapplications related to the D2DSS, a CP length, and the like by using ascheme other than the PD2DSCH. For example, in a partial networkcoverage scenario, UEs out of coverage may not know whether the DM ofthe base station operating in an adjacent area is TDD or FDD. If the UEsout of coverage indiscreetly perform D2D communication without knowingthe DM, reception of the downlink signal of the cell boundary UE may beseriously interfered. Therefore, the D2D terminal should recognize theDM of the cell, which may be directed on the PD2DSCH. Only, there may bea case where the reception of PD2DSCH is difficult (e.g., a case wheredifferent PD2DSCHs are transmitted on the same time resource, and thusthe PD2DSCH cannot be appropriately restored, and the like). Hence, theDM may be directed through the structure of the synchronization signalas will be described below. As another embodiment, the types ofapplications related to the D2D synchronization signal (in this case,the types of application may include a public safety, a D2Dcommunication for a specific purpose, and the like) may be indicatedthrough the structure of the synchronization signal. Namely, the D2DSSformat may be different for each application, which will be describedbelow in detail. In the description below, one of application 1 andapplication 2 may be a public safety. Further, DM1 may be TDD and DM2may be FDD, or DM1 may be FDD and DM2 may be TDD.

Transmission of Automatic Gain Control (AGC) Preamble in D2DCommunication

In the existing cellular communication, a periodically transmittedcell-specific reference signal and the like exist, and thus a separateAGC section is not necessary. However, in the D2D communication, thereis no repeatedly transmitted reference signal such as a cell-specificreference signal, and thus it is necessary to include an AGCstabilization section in the initial period of the D2D signaltransmission. By including the AGC stabilization section in the D2Dsignal transmission, in D2D communication, the UE directly transmits asignal. As such, the point of time of signal transmission, a frequencyresource, and the like may be different for every subframe, therebyreducing the influence of the fluctuation of the average power.

Hereinafter, the scheme of generating an AGC preamble needed in the D2Dsignal transmission will be described. The description below may beapplied to a UE-to-vehicle communication (e.g., a V2X and the like) aswell as the D2D communication.

Structure of AGC Preamble

A D2D UE device according to an embodiment of the present invention maygenerate an AGC preamble by mapping a sequence for the AGC preamble to aresource element and performing an inverse fast Fourier transform (IFFT)on the mapped AGC preamble. At this time, the sequence for the AGCpreamble is repeated N times when mapped to the resource element. Whenthe UE is an in-coverage UE, the N may be proportional to the frequencybandwidth, and the frequency bandwidth may be a system bandwidth (or thetransmission bandwidth of the D2D signal). If the D2D UE is anout-of-coverage UE, the N may not be related to the frequency bandwidth.If the strength/intensity/quality of the signal received by the D2D UEfrom a base station is equal to or smaller than a preset value, the Nmay not be related to the frequency bandwidth or may be a preset value.The N may be set by a network or may have been set to a certain value inadvance. Further, the N may be dependent on the system frequencybandwidth. This may be selectively shown to the out-of-coverage UE. Whenthe N is too big, the distance on the frequency axis becomes large, andthus the use for the purpose of the channel estimation becomesdifficult. Hence, the N may be determined depending on the channel statereport, the transmission/reception signal strength between D2D UEs, andthe like.

Likewise, the D2D UE according to the above-described embodiment of thepresent invention sets a repeated factor to N in IFMDA as AGC preambleso as to be generated and transmitted.

FIG. 5(a) illustrates a process of generating an AGC preamble accordingto an embodiment of the present invention. In FIG. 5, each block refersto an RE to which a sequence for AGC preamble is allocated. As shown inFIG. 5, when the sequence for AGC preamble is mapped to the RE,repetition of N times is applied. After the mapping, an AGC preamble maybe generated by taking IFFT. As another example, nulling may beperformed instead of repetition. Namely, in the frequency domain,mapping may be performed as a comb type and IFFT may be taken. In such acase, a repeated form of the same sequence may be generated in the timedomain. FIG. 5(b) illustrates a generated AGC preamble. As explainedabove, through the repetition of N times and IFFFT, a preamble of anN-times repeated form may be generated. Namely, in the time domain, ashort block is repeated N times. Further, after generating a sequence,by repeating N times in the time domain, the same effects may be shown.

In the case of generating an AGC preamble as described above, thefollowing effects are shown. In LTE system, various frequency bandwidthsof 1.4 MHz to 20 MHz for respective carriers are supported. In thiscase, the length of the section needed in the AGC may be differentdepending on the frequency bandwidth. When it is assumed that the numberof samples needed in AGC for estimation of stable average receivingpower is fixed, the sampling rate becomes different depending on thefrequency bandwidth, and thus the length of the section needed for AGCmay become different. As the frequency bandwidth decreases, the samplingrate decreases, whereby the section length needed for the AGC mayincrease. On the other hand, as the frequency bandwidth increases, thesampling rate increases, whereby the section length needed for the AGCmay decrease. Further, the length of the preamble needed in the AGCsection may be fixed irrespective of the frequency bandwidth. Forexample, one OFDM symbol is fixed and may be used in the transmission ofthe AGC preamble. When the frequency bandwidth is large and the lengthof the preamble used in the AGC section is fixed, the time section otherthan the section needed for the AGC (the section needed for turning AGC)may be used for other purposes (e.g., a synchronization fine tuning,supplementary DMRS, and the like). Namely, when part of the short lengthis used in the AGC and the AGC stabilization section is short dependingon the frequency bandwidth, the signal may be restored in the frequencydomain without ICI by using complete blocks of the remaining area exceptthe AGC. Further, even when only part of the preamble is receivedthrough the above-described AGC generation method, restoration may bepossible in the frequency domain without inter carrier interference(ICI).

In terms of a receiving UE, the receiving operation of the UE may bedifferent depending on the frequency bandwidth. When the frequencybandwidth is large, the AGC section becomes short, and thus if FFT istaken by copying other completely received blocks except the short blockreceived in the time domain to the non-received area, the symbol may becompletely restored in the frequency domain. FIG. 6 explains that therestoration operation may be different depending on the frequencybandwidth. In the small frequency bandwidth, one symbol is entirely usedas AGC, but in a large bandwidth, only some samples are used, andcompletely received part among the remaining areas is copied and thenFFT is taken so that the signal may be restored without ICI in thefrequency domain.

Continually, the method of generating an AGC preamble according toanother embodiment of the present invention will be described.

A single tone signal may be used as the AGC preamble. Namely, each UEmay load information on only one RE in the symbol to be used as the AGC(e.g., an on/off keying or a BPSK/QPSK symbol) and may fill theremaining area with Os. Thereafter, the power applied to the symbol isscaled to be the same as the transmitting power so as to be transmitted.Such a single tone signal is an extreme constant envelope signal and mayshow the best performance in estimating the average power. The powerapplied to the single tone is preferably the same as the power appliedto the D2D signal. Yet, when the ratio is informed to the receiving UEin advance or the power is applied in a predetermined ratio, anotherpower may be set. At this time, with respect to the location of REtransmitted by each UE, all UEs may use a predetermined location or thelocations of REs transmitted by respective UEs may be different. Inparticular, when the locations of the REs are different for respectiveUEs, the receiving UE may recognize the received power and the frequencyat the reception, and thus estimation of the average receiving powerbecomes simple. Namely, if the receiving UE takes correlation from thefrequency tone (RE) having the possibility of appearance of a singletone so as to be combined, the average power may be easily estimated.The location of the RE transmitted for each UE may be a value linked tothe CS or ID of the later transmitted sequence. For example, if the DMRSis later transmitted and the CS is UE-autonomously set, the RE locationof the AGC preamble may have been transmitted from the RE location ofthe CS value (if CS is 4, the single tone is transmitted in RE 4 times).

As another example, a plurality of short preambles may be transmitted inthe time domain. Short preambles are repeatedly transmitted in the timedomain. At this time, the total length of the AGC preamble may be thelength of one OFDM symbol. In the frequency domain, the frequency domainsignal of the short preamble in the time domain may be placed away by NRE. The advantage of such a scheme is that if a preamble is transmittedin the time domain and the preamble has a constant envelope, a constantenvelope signal is shown in the time domain, and thus the average powerestimation in the time domain can be easily performed.

PSS or SSS may be used as the AGC preamble. This is a scheme that may beparticularly used for D2D synchronization signal (D2DSS). When the D2DSSis transmitted as a plurality of PSSs, one of the PSSs or SSSs may beused as the AGC preamble. At this time, the sequence ID of the PSS orthe SSS may be one of the IDs of later-transmitted PSSs or SSSs or maybe a certain ID which has been set differently in advance.

As another example, a DMRS sequence may be used as an AGC preamble.Namely, when a discovery or communication signal is transmitted, a DMRSsequence may be transmitted to a first symbol. At this time, thesequence ID and CS of the DMRS sequence of the AGC preamble may be thesame as those of the later DMRS, or the sequence ID of the DMRS sequencemay be the same as that of the later DMRS, but the CS of the DMRSsequence may be different from that of the later DMRS. Such a linkedrelation may have been predetermined, or the CS of the AGC preamble maybe set through the modulo operation of the DMRS or a predeterminedfunction.

Sequence ID of AGC Preamble

As explained above, the sequence ID of the generated AGC preamble may beset as follows.

The sequence ID for the AGC preamble may have been obtained from thesynchronization source of the D2D UE. Namely, the sequence ID may be asynchronization source ID. This scheme may be applied when thesynchronization source transmits a D2DSS. Further, the ID linked withthe ID of the synchronization source having the UE belong thereto may beused as the ID of the AGC preamble even when a discovery, communication,and scheduling assignment (SA) are transmitted. In such a case, thesequence ID obtained from the synchronization source may be used incommon by the D2D UE receiving the AGC preamble. Namely, UEs belongingto the same synchronization cluster may use the same IE as the AGDpreamble sequence ID. Yet, in this case, there is a possibility that adistorted average power may be estimated due to the offset interferenceof the channel. In order to prevent such a distortion, the ID of thesequence transmitted after the AGC preamble may be linked to the ID ofthe AGC preamble sequence. For example, when the signal transmittedafter the AGC preamble is either a discovery signal or a communicationsignal, the sequence ID may be linked to the sequence ID of thedemodulation reference signal related to the discovery signal or thecommunication signal. In the case of the discovery, the DMRS is to betransmitted. There is a possibility that the cyclic shift (CS) of theDMRS is autonomously set by the UE so as to be transmitted. When thecyclic shift is applied to the generation of the AGC preamble, thecyclic shift may be linked to the cyclic shift of the demodulationreference signal related to the discovery signal or the communicationsignal. When the number of CSs of the AGC preamble is different from thenumber of CSs of the DMRS, the AGC preamble performs the modulooperation on the DMRS CS and uses the result of the operation as the CSof the sequence of the AGC preamble, or sets the CS or sequence of theAGC preamble by a predetermined mapping scheme. For example, when thenumber of sequence IDs of the demodulation reference signal related tothe discovery signal or the communication signal is greater than thenumber of sequence IDs for the AGC preamble, the modulo operation may beapplied to the sequence ID of the demodulation reference signal relatedto the discovery signal or the communication signal.

As another example, the sequence ID may be a group ID. Namely, thesequence ID for the AGC preamble may be used in common in the grouphaving the D2D UE belong thereto.

As another example, the sequence ID may be a pre-configured ID. The AGCis an operation that is performed first before a certain signal isreceived, and thus it is considered that it may be difficult to obtain acertain ID. The pre-configured ID may have been set by a network or mayset the sequence ID of the preamble of the AGC with a preset ID. At thistime, when the same preamble is used for each UE belonging to the samesynchronization cluster, a distorted average power may be estimated bythe offset interference of the channel. In order to prevent such adistortion, the ID of the sequence transmitted after AGC may set to belinked to the ID of the AGC preamble sequence. For example, in the caseof the discovery, the DMRS is to be transmitted, and there is apossibility that the CS of the DMRS is autonomously set and istransmitted. In this case, the ID of the preamble of the AGC or the CSof the sequence of the preamble may be linked to the CS of the DMRS. Ifthe number of AGC preamble CSs is different from the number of CSs ofthe DMRS, the modulo operation may be performed for the DMRS and theresult may be used as the CS of the sequence of the AGC preamble, or theCS or sequence of the AGC preamble may be set by a predetermined mappingscheme.

Further, the transmitting UE IE may be used as the sequence ID. When thesignal of the AGC is transmitted, if different IDs are used forrespective UEs, the offset interference of the channel when collided byusing the same sequence may be prevented. Therefore, the sequence ID ofthe AGC preamble may use the transmitting UE ID for such a purpose.

Further, a random ID may be used. By using a random ID, UEs may havedifferent sequence IDs, which can resolve the offset interferenceproblem of the channel which may occur when the same sequence ID isused.

Whether the above-described embodiments are to be applied may bedifferent depending on the synchronization, SA, D2D communication, andD2D discovery. For example, in the case of the discovery, the AGCpreamble structure uses the repetition of N times, and in the case ofthe synchronization signal, PSS/SSS may be used.

Transmission Band of AGC Preamble

An AGC preamble may be transmitted in the same band as in a D2D signal.The AGC preamble may be a preamble transmitted on the same RB as the RBwhere the D2D signal is transmitted. For example, when thesynchronization signal is transmitted in 6 RB in the center of thesystem bandwidth, the AGC preamble may also be transmitted in 6 RB inthe center. As another example, when a discovery signal is transmittedin RB at a certain frequency location, the AGC preamble may betransmitted as the first symbol of a certain RB.

Further, the transmission band of the AGC preamble may set in advance(e.g., 6 RB in the center of the system bandwidth). The band where theAGC preamble is transmitted may have been predetermined or may beconfigured by a network. When configuration may be performed by anetwork, this may be an area linked to the frequency bandwidth. Forexample, when the frequency band is large, the area where the AGCpreamble may be transmitted together as a large area, and when thefrequency bandwidth is small, the area where the AGC preamble istransmitted may also be set as a small frequency bandwidth. Theadvantage of such a scheme is that because the band where the AGCpreamble is transmitted limited, only the signal of the correspondingband may perform detection and attenuation computation. The operation ofthe AGC may include average power estimation, symbol detection, andattenuation computation. At this time, symbol detection and attenuationcomputation are performed in only the predetermined band, and thus theAGC preamble reception and adaptive operation may become simple.

Further, the sequence used in the AGC preamble may be the same sequenceas the SRS or may be DMRS. Further, the sequence may also be Zadoff-chu(ZC) sequence, gold sequence, m-sequence, or the like.

At this time, the sequence ID and/or the CS used in the AGC preamble maybe linked to the ID (or the seed value of the sequence) of the sequence(e.g., the synchronization sequence in the case of the synchronizationsignal, DMRS in the case of the discovery or communication signal) andthe CS which are transmitted later. For example, the sequence ID of theAGC preamble is the same as the DMRS sequence ID, and the CS may bedefined by a predetermined mapping table or may have a linked relationby the modulo operation. Further, the sequence ID of the AGC preamble isdifferent from the ID of the sequence that is transmitted later, but apredetermined mapping function may be used.

It was assumed in the above description that the AGC preamble uses 1OFDM symbol, but the present invention is not limited thereto. Thepresent invention may be applicable to the case where one AGC preambleuses a plurality of OFDM symbols.

Configuration of Apparatus According to an Embodiment of the PresentInvention

FIG. 7 illustrates a configuration of a transmitting point device and anUE device according to an embodiment of the present invention.

A transmitting point device 10 according to the present inventionincludes a receiving module 11, a transmitting module 12, a processor13, a memory 14, and a plurality of antennas 15. The plurality ofantennas refer to transmitting point devices supporting MIMOtransmission/reception. The receiving module 11 may receive varioussignals, data, and information on the uplink from the UE. Thetransmitting module 12 may transmit various signals, data, andinformation on the downlink to the UE. The processor 13 may controloverall operation of the transmitting point device 10.

The processor 13 of the transmitting point device 10 according to anembodiment of the present invention may process necessary matters ineach of the above-described embodiments.

The processor 13 of the transmitting point device 10 additionallyperforms a function of performing the operation process of informationreceived by the transmitting point device 10, information to betransmitted to the outside, and the like. The memory 14 may store theoperation-processed information and the like for a predetermined timeand may be substituted by a component such as a buffer (not shown).

Referring to FIG. 7 again, an UE 20 according to the present inventionincludes a receiving module 21, a transmitting module 22, a processor23, a memory 24, and a plurality of antennas 25. The plurality ofantennas 25 refer to UEs supporting MIMO transmission/reception. Thereceiving module 21 may receive various signals, data, and informationon the downlink from the base station. The transmitting module 22 maytransmit various signals, data, and information on the uplink to thebase station. The processor 23 may control overall operation of the UE20.

The processor 23 of the UE 20 according to an embodiment of the presentinvention may process matters needed in each of the above-describedembodiments.

The processor 23 of the UE 20 additionally performs a function ofperforming the operation process of information received by the UE 20,information to be transmitted to the outside, and the like. The memory24 may store the operation-processed information and the like for apredetermined time and may be substituted by a component such as abuffer (not shown).

Such a specific configuration of a transmitting point device and an UEmay be independently applied in the above-described various embodimentsor two or more embodiments may be simultaneously applied. Redundantpoints are omitted for clarity of description.

Further, in the description about FIG. 7, the description about thetransmitting point device 10 may also be applied to the relay device asthe downlink transmitting body or the uplink receiving body in the samemanner. The description about the UE 20 may also be applied to the relaydevice as the downlink receiving body or the uplink transmitting body inthe same manner.

Embodiments of the present invention may be implemented using variousmeans. For instance, embodiments of the present invention can beimplemented using hardware, firmware, software and/or any combinationsthereof.

In case of the implementation by hardware, a method according to eachembodiment of the present invention can be implemented by at least oneselected from the group consisting of ASICs (application specificintegrated circuits), DSPs (digital signal processors), DSPDs (digitalsignal processing devices), PLDs (programmable logic devices), FPGAs(field programmable gate arrays), processor, controller,microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code is stored in amemory unit and is then drivable by a processor. The memory unit isprovided within or outside the processor to exchange data with theprocessor through the various means known to the public.

As mentioned in the foregoing description, the detailed descriptions forthe preferred embodiments of the present invention are provided to beimplemented by those skilled in the art. While the present invention hasbeen described and illustrated herein with reference to the preferredembodiments thereof, it will be apparent to those skilled in the artthat various modifications and variations can be made therein withoutdeparting from the spirit and scope of the invention. Thus, it isintended that the present invention covers the modifications andvariations of this invention that come within the scope of the appendedclaims and their equivalents. For instance, the respectiveconfigurations disclosed in the aforesaid embodiments of the presentinvention can be used by those skilled in the art in a manner of beingcombined with one another. Therefore, the present invention isnon-limited by the embodiments disclosed herein but intends to give abroadest scope matching the principles and new features disclosedherein.

While the present invention has been described and illustrated hereinwith reference to the preferred embodiments thereof, it will be apparentto those skilled in the art that various modifications and variationscan be made therein without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention covers themodifications and variations of this invention that come within thescope of the appended claims and their equivalents. And, it isapparently understandable that an embodiment is configured by combiningclaims failing to have relation of explicit citation in the appendedclaims together or can be included as new claims by amendment afterfiling an application.

The above-described embodiments of the present invention may beapplicable to various mobile communication systems.

What is claimed is:
 1. A method of generating a device-to-device (D2D)signal by a user equipment (UE) in a wireless communication system, themethod comprising: mapping a sequence for an automatic gain control(AGC) preamble to a resource element; and generating the AGC preamble byperforming an inverse fast Fourier transform (IFFT) on the sequence forthe AGC preamble mapped to the resource element, wherein the sequencefor the AGC preamble is mapped to the resource element repeatedly Ntimes, and wherein the N is determined based on a frequency bandwidthrelated with the D2D signal.
 2. The method of claim 1, wherein thesequence for the AGC preamble comprises a demodulation reference signalsequence.
 3. The method of claim 2, wherein the demodulation referencesignal sequence has a same sequence ID of a demodulation referencesignal related to a signal transmitted after the AGC preamble.
 4. Themethod of claim 1, wherein a UE receiving the AGC preamble acquiresinformation on the frequency bandwidth of the D2D signal based on the N.5. The method of claim 1, wherein a sequence ID for the AGC preamble isobtained from a synchronization source of the user equipment.
 6. Themethod of claim 5, wherein the sequence ID obtained from thesynchronization source is used in common by a user equipment havingreceived the AGC preamble.
 7. The method of claim 6, wherein when asignal transmitted after the AGC preamble is either a discovery signalor a communication signal, the sequence ID is linked to a sequence ID ofa demodulation reference signal related either to the discovery signalor to the communication signal.
 8. The method of claim 7, wherein when acyclic shift is applied to generation of the AGC preamble, the cyclicshift is linked to a cyclic shift of the demodulation reference signalrelated either to the discovery signal or to the communication signal.9. The method of claim 7, wherein when a number of sequence IDs of thedemodulation reference signal related either to the discovery signal orto the communication signal is greater than a number of sequence IDs forthe AGC preamble, a modulo operation is applied to the sequence ID ofthe demodulation reference signal related either to the discovery signalor to the communication signal.
 10. The method of claim 1, wherein the Nis determined by further considering the signal strength of the D2Dsignal and a channel status report.
 11. The method of claim 1, wherein asequence ID for the AGC preamble is used in common within a group havingthe user equipment belong thereto.
 12. The method of claim 1, whereinthe sequence for the AGC preamble comprises one selected from the groupconsisting of a Zadoff-chu (ZC) sequence, a gold sequence and anm-sequence.
 13. A user equipment device for generating adevice-to-device (D2D) signal in a wireless communication system, theuser equipment device comprising: a receiving module; and a processor,wherein the processor maps a sequence for an automatic gain control(AGC) preamble to a resource element and generates the AGC preamble byperforming an inverse fast Fourier transform (IFFT) on the sequence forthe AGC preamble mapped to the resource element, wherein the sequencefor the AGC preamble is mapped to the resource element repeatedly Ntimes, and wherein N is determined based on a frequency bandwidthrelated with the D2D signal.